106 THE QUANTITATIVE METHOD IN BIOLOGY 



each corner of each cell. This is a mechanical impossibility, 

 because the cell-walls always meet each other three by three. 

 Therefore a supplementary (more or less curved) facet is always 



Fig. 15. — Chess-board system in leaves of mosses. — i. Cathannea 

 undulata, almost regular. 2. Id., id., slight disorder. 3. Mnium 

 undulatum, disoTdei. AdncUuyam 



interposed at each comer : an alteration of the form of the 

 cells and a certain degree of disorder are unavoidable con- 

 sequences of this interposition. The cause of disorder is 

 imiversal, but its effects are ordinarily rather unimportant. 

 (Fig. 8.) 



